Bonii!

If you specify a non-default theme in Firefox then that theme will override the GTK preference.

Some of the GTK theme bleeds through into Firefox regardless of your Firefox-theme choice. For example, Xfce-dusk is a reasonable (but imperfect) dark theme. But in Firefox when you edit a WordPress post the default text is white. The background colour stays white, so you can’t read much. =/

To fix that, you must change your theme back to something else, like ClearLooks, and reload the page in Firefox.

The "make site visible" Greasemonkey script can help with website colours for general surfing. What a WONDERFUL tool. I think it’s unfinished/bugged though.